Field of the Invention
This invention relates to the keyslide mechanism of a pushbutton radio receiver and particularly to the memory cam located therein.
Pushbutton tuning is a convenience found on many radio receivers. In a standard automotive type pushbutton radio there is provided a plurality of pushbutton operated keyslide mechanisms for adjusting the frequency of operation of the receiver. Such mechanisms are well known in the art and a detailed description thereof may be found in U.S. Pat. No. 3,195,359 to Clark. Basically, pivotally mounted on the keyslide mechanism is a memory cam which can be frictionally locked at a preselected angle when the pushbutton is pulled outwardly and then returned to a normal position.
The cam has a pair of opposing faces which engage parallel rods of a treadle bar assembly, rotating the assembly to the locked cam angle. Assembly rotation in turn shifts the position of the tuning core carriage of the receiver. Movement of the carriage repositions the tuning cores of the receiver with respect to stationary tuning coils provided therein, thereby to change the frequency of operation of the receiver.
Presently, the memory cam has linear engaging faces, which, when the pushbutton is depressed, make contact with the treadle bar rod at an angle dependent on the initial position of the rod and the locked angle of the cam. As the pushbutton is further depressed, two forces are transmitted from the cam face to the rod. The first force is tangential to the rotational arc of the assembly thus causing assembly rotation. The second force acts through the axial center of the rod towards the axis of rotation of the assembly tending to compress the assembly. As the second force does not rotate the treadly assembly, it undesirably results in a requirement for increased pushbutton pressure. For small angles of treadle bar rotation, the linear cam face exerts a substantial tangential force on the rod and the required pushbutton force is not excessive. However, for large rotations, a considerably greater force is required, as the rotational force component is reduced by a substantial compressional force component. This is undesirable since an inadequate tangential force results in receiver mistuning.